The WO 2013/105025 A1, which is incorporated into the present text by reference, describes a device and a method for optically controlling the iterative incorporation of fluorescently labeled nucleic acids into a molecule attached to the surface of a wiregrid substrate. Based on a strong optical confinement of excitation light and of cleavage light by evanescent waves, the sequencing reaction can be read-out without washing the surface. Stepwise sequencing is achieved by using nucleotides with optically cleavable blocking moieties. After read-out the built in nucleotide is deblocked by cleavage light through the same substrate. This ensures that only bound nucleotides will be unblocked.